1. Field of the Invention
This invention concerns the improvement of a fundus camera which takes photographs by means of a fluorescent agent, and which can eliminate harmful reflected light.
2. Description of the Prior Art
A fundus camera is known in the art which takes photographs by means of a fluorescent agent. This fundus camera comprises an exciter filter in the illuminating optical system, and a barrier filter is also provided in the photographic optical system. The fundus is illuminated by illuminating light in a specific wavelength range in the illuminating light that has passed through the exciter filter. A fluorescent agent flowing in the blood vessels of the fundus is excited by this illuminating light in a specific wavelength range, and emits fluorescence. The fluorescence from the fundus passes through the barrier filter to be guided to a film or other recording means, and an image of the fundus is thereby recorded on the recording means.
A plate having a black spot in its center is interposed in the optical path of the illuminating optical system so as to eliminate harmful reflected light from the surface of the objective lens. If there were no black spot, part of the illuminating light reflected from the surface of the objective lens would pass through the aperture diaphragm of the photographic optical system so as to reach the film or other recording means. In other words, illuminating light reflected from the surface of the objective lens, which is harmful reflected light, would reach the recording means and lead to deterioration of the image of the fundus photographed by fluorescence. If such a black spot is provided, the illuminating light which is the cause of this harmful reflected light is prevented from reaching the objective lens. Further, an image of the black spot is formed at the position of the aperture diaphragm of the photographic optical system.
However, in this conventional fundus camera which takes photographs using a fluorescent agent, the black spot is interposed in the illuminating optical system. Part of the illuminating light is therefore cut off by the black spot, and a dark shadow of the spot appears in the center region of the fundus image which is undesirable.